Email service providers like ConvertKit, Drip, and Postmark monitor spam complaints closely. If the percentage of complaints exceeds a limit, the IP address can get blacklisted, affecting the email deliverability of others on the service. Google Workspace allows setting up aliases, but DKIM alignment can only be done with the main domain, not aliases. It is essential to have DKIM or SPF, and ideally both, for effective email deliverability.